Protecting means for electrical distribution systems.



G. A. BURNHAM. PROTECTING MEANS FOR ELECTRICAL DISTRIBUTION SYSTEMS.

APPLICATION FlLED NOV 27.191l. I v v Paiented Dev. 28, 191;).

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G A. BURNHAIVI. PROTECTING MEANS FOR 5150mm msrmsunow SYSTEMS.

APPLICA HON FILED NOV 27,191].

Patented Dec. 28, 191:).

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GEORGE A. BURNHAM. 0F SAUGUS, MASSACHUSETTS, ASSIGNOR, BY MESNE ASSIGN- MENTS, TO GENERALELECTRIC COMPANY, A CORPORATION OF NEW YORK.

PROTECTING MEANS FOR ELECTRICAL DISTRIBUTION SYSTEMSL Application filed November 27, 1911.

T 0 all whom it may concern.

Be it known that I, GEORGE A. BURNHAM, a citizen of the United States, residing at Saugus. in the county of Essex and State of Massachusetts, have invented an Improvement in Protecting Means for Electrical Distribution Systems, of which the following is a specification.

One of the well-known types of electricaldistribution systems in use at the present time involving transformers arranged in multiple, and also the type usually termed a ring-system, has protecting-means for sections of the systems, which, in the first instance above noted, comprises overload switches, tripping-magnets therefor, and current-transformers. arranged respectively at opposite ends of each section to be protected, and a circuit connecting the secondary-coils of the transformers in opposition, which may include the tripping-magnets. The protecting-transformers, which are usually currenttransformers, when thus connected in circuit operate under open circuit conditions. there being no energy in the secondary or protecting circuit, and, for this reason .the ordinary or standard current transformers cannot be used, as they heat excessively, thereby destroying the insulation and finally result in failure to ope ate. Hence. specially constructed transformers are required. In many cases indicating and recording instruments are employed, and additional transformers are necessary for these instruments on account of inaccuracies in the specially constructed transformers.

My present invention relates to protecting-means for these types for an electricaldistribution system, and has for its object to so improve thesame that standard current transformers may be used.

The invention consists essentially in providing a protecting-circuit which extends throughout the length of the section of the system to be protected, having trippingmagnets or relays which serve as equivalents therefor, for switches in the current-circuit at the ends of the section, said protectingcircuit being inductively connected with said section by current-transformers, the secondary coils of which are arranged in the protecting-circuit in series relation and in opposition to each other, at opposite ends of the section, said protecting-circuit having shunts for the secondary coils arranged be- Specification of Letters Patent.

Patented Dec. 28, 1915.

Serial No. 662,708.

tween said coils and the tripping-magnets, so that the trippinganagnets are normally included in an inactive portion of the protecting-circuit and are normally de'nergized, and relay-switches controlling said shunts, the magnets of which are arranged in series relation with the secondary coils and on the same-side of the shunts, and the switches of which are included in said shunts, said relay-switches being adapted to be operated by means responsive to an overload, or an abnormal condition of the system which results in an overload, to open the shunts. thereby to include the transformers in circuit with both tripping-magnets, or relays which serve as equivalents therefor.

By means of my improved protecting-circuit each current-transformer. is normally shunted, and therefore has a normally closed secondary-circuit of its own and will not become heated, so that standard transformers may be employed. \Vhen my improved protecting-means is connected with a section of a system wherein the potential or power transformers are arranged in multiple, or with a section of a ring-system, or other system where the opportunity is offered for the current to feed back in case of trouble, then upon the feeding back of the current, the current in one of the protecting-transformers will be reversed. and thereby flow in the same direction as the current in the other protecting-transformer, so that the two protectirig-transformers will act cumulatively and cause both tripping-umgnets to operate. Figure 1 represents in diagram a portion of a well-known type of electrical distribution system, wherein power transformers are arranged in multiple, and provided with protecting-means embodying this invention. Fig. 2 represents in diagram a portion of another well-known type of electrical distribution system provided with my improved protecting means.

Referring to Fig. l of the drawing, 10 represents a generator whose neutral point is grounded at 12; 13, 14: and 15 are busbars connected to the generator; 16 and 17 represent two banks of power-transformers, the prin'iaries of which are connected by wires 18, 19 and 20 with the aforesaid busbars, and the secondaries of which are connected by wires 3.1. 22 and 23 with the bushars 24, 25 and 26. From said bus-barsll. 25 and 26 wires 27, 2S and 29 are'here shown as leading to what is ordinarily called a ring distribution system, shown in diagram in Fig. a, which. as here shown, comprises wires 30, 31 and 32, from which numerous feed-wires lead, although said wires a7, 28 and 229 may lead to any other type of system. The systems thus briefly described are wellknowntypes of electrical distribution systems now in use. Said systems are here shown for the purposes of illustrating my invention as tri-phase. but my improved protecting-means is applicable to single-phase systems as well as to polyphase systems.

My in'iproved protecting means is applicable to different sections of the systems. and, for purposes of illustration, it is herein rep,- resented as applied to the transformer section including transformers 16 and 17, see Fig. 1, and to a section of the ring-system shown in Fig. 2. The several protectingmeans employed are similarly constructed and one will now be described.

Referring to Fig. 1, overload switches 40 and 50 are arranged respectively in the wires l8, l9 and 20, and in the wires 21, :22 and 23, at each end of a section, as for instance, at opposite sides of the bank of transformers 16. Said switches are of any wellknown or suitable construction and adapted to be operated automatically, respectively, by tripping-magnets i1 and 51 or other usual or suitable means. In each of said wires standard current-t ansformers are arranged, as 42, 52, the secondary-coils of which are connected in series relation in a circuit 60, and said secondary-coils, at each end of the section, are arranged in opposition, so that their currents are bucking, so to speak, there being no current passing over the circuit 60, but said transformers will heat excessively and becomes destroyed unless means are provided to prevent such action. Therefore, to prevent such action, yet permit of the employment of standard current transformers, the secondary-coils, at each end of the section, are normally shunted, that is to say, the circuit is provided with shunts 43, for said secondarycoils, thereby to enable each bank of currenttransformers 42, 52 to have a closed secondary circuit of its own, over which the current freely passes, although that portion of the circuit 60 between the shunts is to all intents and purposes dead. Each shunt 43 and 53is controlled by a relay-switch, the switches 44, 54, of which are normally closed to close the shunts and the controlling-magnets 45, 55 of which are connected in the circuit 60, but normally shunted with the secondary coils, so that the controlling-nmagnet of each relay-switcli is responsive to the current passing over the secondary circuit in which it is contained. The tripping-magnets 4.1, 51 are arranged in the circuit 60, but outside of the shunts 43, 53, and being in the inactive portion of said circuit are not responsive until such time as the relayswitches are operated and the shunts opened and the secondary-coils of the transformers thereby included in said circuit. The same protecting-means is provided for the transformers 17; and also for any portion or sec tion of the circuit which it is desired to protect, as for instance, as shown in Fig. 2, so that a detailed description of each protecting-means unnecessary.

()ne illustration of the operation of my improved 1)rotectiug-means is here given. Assuming that a short-circuit occurs on the secondary-circuit of the transforn'ier 16, as indicated by dotted lines at (35, between the wires 21 and 22. then the current in the secondary-coil of the transformer 52 will immediately be reversed by reason of the current flowing back from the t'ansformer 17, through the bus-bars 2%, 25, 2G, and will rise in said transformer 52. and will also rise in the transformer 4:2, and likewise in their secondary circuits. and if of sufiicient value will cause the controlling-magnets i5 and 55 of the relay-switches to lift the members 44, and 5* thereby to open both shunts a3 and 53, and include the transformers 42 and 52 directly in the circuit 60. As the current at this time is reversed in the transformer 52, said transformers l2 and will now act cunmlatively and cause both tripmug-magnets 41 and 51 to respond, to operate both overload-switches. The transformer in will thus be entirely disconnected but the remaining portion of the system will continue in operation. The overloadswitches connected with the transformer 17 will not operate because the current will continue to flow through their protecting transformers in opposite directions, and even if the current should rise in the secondaries of said transformers and the relay-switches should open the shunts, the tripping-magnets will not respond for the reason that the current of each secondary nullifies the other, and remains at zero. A fault or ground in any wire is similar to a short circuit in a single phase of a tri-phase system, and the operation of the system will be the same, with the exception that the current flows through the earth instead of the Wires. \Vhen the overload (vases the relay-switches will be caused to resume their normal positions by means of the tension springs 47, 57, connected to their switch members, thus restoring the parts to normal.

This protecting-means is particularly applicable to a ring-system of electrical-distribution, because the operation is dependent upon the reversal of current in one of the current-transformers adjacent the point where the trouble occurs, yet at such time flowing in the same direction in the other transformers as it did before the trouble occurred, as in a ring-system it will be understood that the current flows in two directions to a fault. The ope -ating-means is applicable to other systems of electrical-distribution for the protection of single transformers not connected in a circuit where the current can feed back and in such case both tripping-magnets will be caused to respond to the operation of either transformer and open both overload-switches. In such case the present protecting-means is of advantage for the reason that the potential of both protecting-transformers need not be suiiiciently great to cause the current to flow through the other transformer, it being shunted at the moment of operation.

I claim 1. In a protective device for systems of distribution, the combination, with a line conductor and a circuit breaker for said conductor having electro-responsive tripping mechanism comprising a coil, of two current transformers at different points on said conductor with their primary windings connected in series through said conductor and their secondary windings connected in series through said coil and in opposition to each other, and electroaesponsive means associated with each transformer for normally maintaining a conducting connection in shunt to the terminals of the secondary winding of said transformer and in series with said coil and for opening said connection in response to current flow through said conductor in excess of a determinate amount.

2. In a protective device forsystems of distribution, the combination with a line conductor and a circuit breaker for said conductor having electro-responsive tripping mechanism comprising a coil, of two current transformers at different points on said conductor with their primary windings connected in series through said conductor and their secondary windings connected in series through said coil in opposition to each other, a normally closed shunt around the secondary winding of each transformer, and relays responsive to a determinate current flow through said conductor for opening said shunts around said transformers and thereby energizing said coil.

3. The combination of a transmission line, two automatic circuit breakers at different points of said line having electro-responsive tripping mechanism comprising a coil, current transformers in each phase at different points with their primary windings connected in series and the secondary windings connected in opposition to one another and in series with both said coils, normally closed shunt circuits in parallel to the secondary windings of said transformers and in series with each other and with said coils, and means responsive to a predetermined current flow in each phase. for opening said shunt circuits around said secondary windings.

4. A protective device for distribution systems comprising an automatic circuit breaker having electro-responsive tripping mechanism comprising a coil, two current transformers at different points in each phase of the system with their primary windings in series with said phase and their secondary windings connected in series with said coil and in opposition to each other, a shunt circuit in parallel with each secondary winding and in series with said coil, and a relay switch associated with each transformer for opening the shunt circuit around said transformer in response to current flow of a predetermined amount through said transformers.

5. A protective device comprising a circuit breaker having a trip coil, two transformers with their primary windings connected in series with each phase of the circuit through said circuit breaker and their secondary windings connected in series with each other and with said coil to impress opposed electromotive forces on said coil when the direction of energy flow through both transformers is the same, and a normally closed relay switch comprising cooperating contacts connected to form a short circuit for the secondary winding of each transformer when said switch is closed and electro-responsive actuating means connected in series with the secondary winding of each transformer between the switch contacts and the transformer for separating said contacts in response to abnormal current flow through said transformer.

In testimony whereof, I have signed my name to this specification, in the presence of two subscribing witnesses.

GEORGE A. BURNHAM. Witnesses:

B. J. NoYEs,

H. B. DAVIS. 

